1. Field of the Invention
The present invention relates to an operation device for operating a hydraulic master cylinder by motor drive.
2. Prior Art
In a transmission of an automobile, utilization of so-called automatic hydraulic pressure generator is known where a friction clutch is connected or disconnected by a hydraulic master cylinder operated by a computer-controlled motor. In such an automatic hydraulic pressure generator, an operation device for operating a hydraulic master cylinder by a motor is disclosed in DE-A No. 4433824. In the constitution of the operation device, a worm is provided on an output shaft of a motor, and a piston rod of the hydraulic master cylinder is connected by a pin to a worm wheel meshing with the worm. According to such constitution, rotation of the motor is reduced by the worm and the worm wheel and thereby torque is increased. Further, by utilizing the lever ratio due to the difference of the distance between the rotation center of the worm wheel and the connection point of the piston rod and the distance between the rotation center of the worm wheel and the meshing point of the worm and the worm wheel, the torque is increased and the rotary motion of the worm wheel is converted into the linear motion of the piston rod.
However, since the operation device in DE-A No. 4433824 intends to increase the torque utilizing the meshing of the worm and the worm wheel, although large force can be applied to the piston rod, it is disadvantageous that the motion of the piston rod is slow, the hydraulic cylinder can not operate rapidly and the responsibility of control to connect and disconnect the friction clutch is deteriorated.
Further, since the worm and the worm wheel mesh with each other substantially in point contact and the pressure is concentrically applied in the worm axis direction to the meshing point of the worm and the worm wheel, it is disadvantageous that the durability of the worm is liable to deteriorate.